This invention relates to an access request control system for one or more access requesting units in a computer system making accesses to a memory, more particularly, to a memory with a high speed, small capacity buffer storage (BS) and low speed large capacity main storage (MS).
Access to memory is conventionally made by an access request from each access requesting unit which is sent to a corresponding register. When access requests compete, one of the access requests is selected in accordance with a priority determination method. Once an access request is selected, BS is accessed. If BS does not have the desired data, MS is accessed. The access to MS requires a considerably longer period of time than an access to BS.
In the prior art, an access request is held in the register while MS is accessed and the corresponding access requesting unit can not issue the next access request during such holding period. Therefore, even when the next access request data exists in BS, such data in BS can not be accessed until the preceding MS is accessed, resulting in poor efficiency.